In recent years, the speeds of railroad cars, particularly on passenger transit vehicles, have dramatically increased. One of the former braking systems which was utilized on these new high speed vehicles is schematically shown and described in Japanese Patent Publication (Kokai) 2-262,459. An example of such a braking system is shown in FIG. 2 of the subject application. In viewing FIG. 2, it will be seen the system includes a brake command controller 1 having an operating handle 1a which is located within easy reach of the engineer or train operator. The operating handle 1a is manually moved or rotated to one of a plurality of selected positions to initiate the desired braking control level or brake command request. The particular position of the rotatable handle la is converted into an electrical signal by a suitable encoding device and is conveyed to a conductive command line 2. The electrical lead 2 is connected to a brake control unit 3 which converts the above-mentioned electrical brake command signal into a proportional air pressure signal. The pneumatic signal Bca is responsive and proportional to the load and/or the rotational speed of the railway vehicle. A plurality of the wheels booster cylinders 5 receives and converts the pneumatic pressure signal Bca into a proportional hydraulic pressure signal Bco. The hydraulic pressure signals Bco are fed to the respective pair of brake cylinders 4. That is, the four booster cylinders 5 are connected to each of the four pairs of brake force cylinders 4 carried by a single railroad car. Namely, the eight brake force cylinders 4 are arranged in pairs for each of the four individual booster cylinder 5.
As shown in FIG. 3, each booster cylinder 5 receives the pneumatic pressure signal Bca obtained from the above-mentioned brake control unit 3. The pneumatic pressure signal Bca is conveyed to a pneumatic cylinder chamber 13 of a pneumatic cylinder 11 via a valve 10. The pneumatic cylinder 11 includes a piston member 14 which is urged against the compressive force of a return spring 15. A piston rod 16 which is integral with the piston 14 displaces the oil into hydraulic cylinder chamber 17 so as to produce an oil pressure signal Bco. This hydraulic pressure signal Bco is transmitted to a brake force cylinders 4 via an anti-skid control valve 18 for developing an appropriate brake force. As shown in FIG. 3, the reference numeral 19 designates an oil reservoir. The brake force cylinders 4 are hydraulic devices which are normally employed in a conventional railway disc brake system.
The type of brake disc which is suitable for use in a railroad disc brake assembly is a conventional brake disc as used on standard railroad systems. However, as the speed of the railroad cars is increased, the conventional disc brakes prove to be inadequate, because they are unable to develop sufficient braking force to control the fast moving vehicles. The heat capacity of conventional brake shoes is insufficient, and secondly the coefficient of friction of conventional brake shoes falls sharply.
Accordingly, it is proposed to solve these problems by increasing the number of the above-described disc brake assemblies. However, such a solution normally requires an extremely large quantity of pressurized fluid for supplying the brake control units and to the booster cylinders. Also, such a proposal leads to the increased overall dimensions of the braking equipment. Another solution has been proposed in which to maintain a coefficient of friction at a certain value even at high temperatures by using new materials for brake discs and brake pads, such as carbonaceous-type materials. However, it has been found that these materials which possess resistance to heat normally have an unstable coefficient of friction, when the temperature of the brake disc falls during low speed running. This, in turn, results in an unstable braking force at low or moderate speeds.